Screwworm Myiasis

Gusanos, Mosca Verde, Gusano barrendor, Gusaneras

Center for Food Security and Public Health Iowa State University - 2004

OverviewOverview

• Organism• Economic Impact• Epidemiology• Transmission• Clinical Signs• Diagnosis and Treatment• Prevention and Control • Actions to take

The Organism

Center for Food Security and Public Health Iowa State University - 2004

Screwworm MyiasisScrewworm Myiasis

• Larvae of the family Calliphoridae−Chrysoma bezziana (Old World)−Cochliomyia hominivorax (New World)

• All warm-blooded animals−Rarely infects birds

• Can occur in any open wound

Importance

Center for Food Security and Public Health Iowa State University - 2004

HistoryHistory

• 1852: First reports of New World Screwworm

• 1958: Development of sterile male technique

• 1966: U.S. free of Screwworm• 1991: Mexico declared free• 2003: Sterile fly facility established in

Panama

Center for Food Security and Public Health Iowa State University - 2004

Screwworm flies mate once in a lifetime, and if one of the insect pair has been sterilized with gamma rays, neither will reproduce.

Center for Food Security and Public Health Iowa State University - 2004

Economic ImpactEconomic Impact

• Reintroduction- $540 million/year−Producer loss−Lost meat supply for export

• Eradication - $1.27 billion−Control costs−Economic impact

Epidemiology

Center for Food Security and Public Health Iowa State University - 2004

Geographic DistributionGeographic Distribution

• Western Hemisphere−Only the New World screwworm−Central and South America−Caribbean Islands

• Eastern Hemisphere−Only the Old World Screwworm−Found in remaining tropical and sub-

tropical areas −Never established in Europe, North

Africa, the Middle East or Australia

Center for Food Security and Public Health Iowa State University - 2004

Morbidity/ MortalityMorbidity/ Mortality

• Mobidity variable−Varies with conditions−Near 100% of newborns in favorable

environment• Mortality varies with treatment

− If treated rarely leads to death−Untreated almost always results in

death

Transmission

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Animal TransmissionAnimal Transmission

• Female fly deposits eggs into wound• Larvae feed on living tissue• Multiple infestations in one wound

are common• Non-contagious• Importation of infected animals

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Human TransmissionHuman Transmission

• Infected in same manner as animals• Can transmit adult screwworms to

nonendemic areas

Animals and Screwworm Myiasis

Center for Food Security and Public Health Iowa State University - 2004

Clinical SignsClinical Signs

• Larvae visible in wound by 3 days−May be hundreds present

• Bloody discharge• Foul-smelling odor• Depression• Off feed• Separation• Attempt to control discomfort

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Post Mortem LesionsPost Mortem Lesions

• Death often occurs when untreated−Allows for multiple

infestations• Result of secondary

infection−Smaller animals more

susceptible

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SamplingSampling

• Before collecting or sending any samples, the proper authorities should be contacted

• Samples should only be sent under secure conditions and to authorized laboratories to prevent the spread of the disease

Center for Food Security and Public Health Iowa State University - 2004

Clinical DiagnosisClinical Diagnosis

• Suspect in any animal with signs• Differentials include any fly larvae

that infest wounds−Several types may be present

• Samples to collect−Larvae from the deepest portion of

wound

Center for Food Security and Public Health Iowa State University - 2004

Laboratory DiagnosisLaboratory Diagnosis

• Microscopic examination− Identification of larvae

• Careful sample collection and handling−70% alcohol

• ELISA tests in development

Center for Food Security and Public Health Iowa State University - 2004

Treatment Treatment

• Obtain samples first• Topical application of larvicide

−2-3 successive days• Spray or dip with organophosphate

−Prevents reinfestation

Screwworm Myiasis in Humans

Center for Food Security and Public Health Iowa State University - 2004

Clinical Signs in HumansClinical Signs in Humans

• Larvae visible within wound• Bloody discharge• Foul-smelling odor• General discomfort

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Post Mortem LesionsPost Mortem Lesions

• Untreated wounds will enlarge−Can extend into body cavities

• Death unlikely unless untreated−Result of secondary infection

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DiagnosisDiagnosis

• Laboratory Tests−Microscopic examination of

Larvae identification

−Differentials include any fly larvae that infest wounds

−ELISA

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Treatment Treatment

• Removal of larvae• Debridement, if necessary• Good hygiene

Center for Food Security and Public Health Iowa State University - 2004

Public Health SignificancePublic Health Significance

• Humans are susceptible−138 cases in Nicaragua−530 cases in El Salvador

• Use proper precautions if screwworm is suspected

Prevention and Control

Center for Food Security and Public Health Iowa State University - 2004

Recommended ActionsRecommended Actions

• Notification of Authorities−Federal:

Area Veterinarian in Charge (AVIC) www.aphis.usda.gov/vs/area_offices.htm

−State veterinarian www.aphis.usda.gov/vs/sregs/official.htm

• Treat infested wounds with larvicide• Suspend animal movement

Center for Food Security and Public Health Iowa State University - 2004

Disinfection/VaccinationDisinfection/Vaccination

• Destruction of larvae• Larvicide in infested wounds• Organophosphates• No vaccine available

Center for Food Security and Public Health Iowa State University - 2004

PreventionPrevention

• Surveillance in nonendemic areas−Prevent importation

• Frequent animal inspections in endemic areas−Organophosphate treatment

• Seasonal avoidance

Additional Resources

Center for Food Security and Public Health Iowa State University - 2004

Internet ResourcesInternet Resources

• World Organization for Animal Health (OIE) website−www.oie.int

• USAHA Foreign Animal Diseases – “The Gray Book”−www.vet.uga.edu/vpp/gray_book/index

• USDA-APHIS Veterinary Services−www.aphis.usda.gov/vs

Acknowledgments

Development of this presentation was funded by a grant from the Centers for Disease Control and Prevention to the Center for Food Security and Public Health at Iowa State University.

Author:

Co-authors:

Reviewer:

Elise Gingrich, BS

Anna Rovid Spickler, DVM, PhDRadford Davis, DVM, MPH, DACVPM

Bindy Comito Sornsin, BA

Acknowledgments